1. Field of the Invention
The present invention relates generally to an occupant restraint system of the type having a confinement which is expanded by a fluid supply to restrain movement of an occupant of a vehicle during a collision. Such a system is illustrated and described in U.S. Letters Patent 3,516,685 and 3,602,527.
2. Description of the Prior Art
The expandable confinement, commonly referred to as an air bag or air cushion, has a collapsed inoperative condition for storage in a steering wheel, dashboard or other location within a vehicle at a position generally forward of a normal occupant position. Upon the sensed occurrence of a collision of the vehicle, expansion of the confinement is generally effected by a fluid supply in the form of a pressure vessel having a single chamber of stored pressurized gas. The stored gas is released from the chamber by rupturing a portion of the pressure vessel which communicates with a gas directing means, such as a diffuser, communicating with the interior of the confinement. The single chamber stored gas fluid supply performs satisfactorily in most instances.
Although such an occupant restraint system appears to be simple in construction, its operational parameters are extremely sophisticated. For example, during operation of an occupant restraint system the confinement must become fully expanded within one hundred milliseconds or less from the time a collision condition of the vehicle is sensed in order to restrain the occupant of the vehicle and prevent injury. This restraint is accomplished in the prior art stored gas systems by rapidly opening the single chamber of highly compressed stored gas, such as nitrogen at a pressure of approximately 3600 psi, and directing the gas into the confinement after the sensing of a collision condition. The rapid opening of a single chamber of stored gas results in an extremely high mass flow rate of gas into the confinement during the first few milliseconds after the chamber has been opened. The flow rate of gas thereafter decreases as a function of the pressure decrease in the chamber. The rapid expansion results in a relatively high stress being placed on the confinement, a high momentum being transferred to the confinement and a relatively loud noise. The reduction of this stress, momentum and noise would be beneficial to confinement construction and cost and system performance and effect.